1. Field of the Invention
This invention relates to improved attenuating apparatuses of the type used in the manufacture of flat glass having a nip sensing device, a linear movement monitoring device and an angular movement monitoring device which are used in combination to (1) maintain nip width within a predetermined range; (2) maintain the width of the glass within a predetermined range; and (3) center the glass in the forming chamber.
2. Discussion of the Technical Problem
In the practice of manufacturing flat glass, molten glass is moved through a delivery channel onto a molten bath of tin and a ribbon of glass is caused to form which is drawn and pulled along the bath and gradually cooled until it becomes dimensionally stable. Thereafter the glass ribbon is removed from the bath and is fed to an annealing lehr through which it passes to anneal the glass.
When supported on molten metal, molten glass naturally stabilizes on the molten bath of tin at a thickness of about 0.271 inch (6.87 millimeters). This thickness is called equilibrium thickness and in the absence of a controlled application of forces to the glass during forming, glass formed on tin thus obtained, has this thickness when cooled.
Glass less than equilibrium thickness can be obtained by pulling the glass by a force downstream of the delivery channel or near the lehr (often called lehr force) which stretches or attenuates the glass and causes it to move faster than when glass of equilibrium thickness is produced. However, the glass ribbon not only becomes thinner, it also becomes narrower unless the edges of the ribbon are restrained as by using edge roll machines, i.e., attenuating apparatus such as the type disclosed in U.S. Pat. No. 3,709,673.
In general, the attenuating apparatus includes an attenuating wheel that engages the upper surface of the body of hot glass. The angle subtended by the axis of the attenuating wheel and the glass path defines an angle of attenuation that has positive degrees when the axis of the attenuating wheel is angled toward the delivery channel.
A pair of opposed attenuating apparatuses have their respective attenuating wheels applying longitudinal and transverse forces to maintain the ribbon within a desired width.
Although the attenuating apparatuses used in the art are ideally suitable for applying longitudinal and transverse forces to the molten body of glass to provide a glass ribbon of a desired width, there are limitations. More particularly, the apparatuses are not provided with a nip sensing device which maintains the nip width within a predetermined range. The nip width as the term is used herein, is defined as that distance between the attenuating wheel and the edge of the ribbon. Maintaining the nip width within a predetermined range is desired. This is because the attenuating wheel which engages the upper surface of the ribbon leaves a wheel mark which makes that portion of the ribbon unusable. Further, during attenuation of the glass, the glass tends to neck down, i.e., decrease in width. If one of the pair of attenuating wheels disengages the glass, the other attenuating wheel tends to pull the glass toward itself. When this occurs, the ribbon jams against the sidewall of the container for the molten metal.
Further, the attenuating apparatuses of the prior art are not provided with a system for maintaining the ribbon in the center of the bath. This is desired when it is realized that a more uniform heating from the center toward the edges of the ribbon is obtained when the center of the molten glass is centered in the bath.
Still further, the attenuating apparatuses of the prior art are not provided with facilities which continually monitor and adjust the attenuating angle to maintain the width within a predetermined range. More particularly, as the molten glass moves along the supporting molten metal, the width varies. By maintaining the width within a predetermined range by automatically adjusting the angle of attenuation a more uniform ribbon width can be achieved.
Although in the prior art there are various types of apparatuses which can determine the boundary between the glass edge and the molten tin, for example, U.S. Pat. Nos. 3,764,285; 3,805,072; and 3,794,477, the apparatuses are used separately and are not integrally attached to an attenuating apparatus. In most instances, the devices of the prior art which determine the boundary between the glass and molten bath are bulky in size and are not easily attached to the attenuating apparatuses.
It would be advantageous therefore if an attenuating apparatus of the type used in the rior art were provided with facilities to determine nip width, ribbon width, and center the ribbon in the molten bath.